Several types of devices which are adapted to provide indications of the performance of reciprocally moving parts are known in the prior art. For example, U.S. Pat. No. 4,509,901 to McTamaney et al. discloses an apparatus for detecting problems in sucker-rod well pumps, which includes a first transducer which is located between an upper end of a sucker-rod string and a lower end of a cable section. U.S. Pat. No. 3,343,409 to Gibbs discloses a method of determining sucker rod performance in which a strain-gauge load cell is connected to a polished rod to measure the polished rod load. Also, U.S. Pat. No. 4,363,605 to Mills discloses an apparatus which generates an electrical signal which is proportional to the tension in a bridle which supports a string of a sucker rod. The apparatus includes a load cell between two arms which are attached to two bridle cables and which place the load cell in compression, so that the load cell generates an electrical signal proportional to the force needed to spring the cables apart from each other. The apparatuses of the above-mentioned patents each have the disadvantage, however, that they involve relatively complex electrical measurement and/or computation, and thus tend to be relatively complex and expensive to manufacture.
Other devices are known in the prior art which provide continuous indications of a weight on a drill bit. For example, U.S. Pat. No. 2,703,008 to Seljos et al. discloses a weight-on-bit indicating apparatus which includes a weight responsive device attached to a line of a well drilling rig. The weight responsive device generates a pressure signal to three diaphragms which are pressure-balanced such that the weight on a bit of the well drilling rig registers on a gauge. Also, U.S. Pat. No. 2,696,111 to Conner discloses a drill string weight indicating apparatus which includes a roller to which force is applied by a drill string, a diaphragm which is connected to the roller and which closes a chamber, and a pressure gauge connected to the chamber to indicate the load on the drill string based on the pressure in the chamber. These devices have the disadvantage, however, that they are designed for use with a drill string which moves slowly past the devices in one direction only. Thus these devices are of little use in providing an indication of the variation in load on a reciprocally moving part.
One device is known in the prior art which provides an indication of the pressure in an apparatus, wherein the apparatus includes a reciprocatingly moving part. U.S. Pat. No. 4,417,236 to Huno discloses an overload detecting device for a hydraulic jack which includes a pressure sensitive switch member having a piston-like member in a housing. The piston-like member communicates with a duct of the hydraulic jack and is biased in one direction by a spring. If the pressure in the duct rises above a predetermined value, the pressure overcomes the bias of the spring, and the piston-like member contacts a spring plate to set off an alarm. One of the disadvantages of this device, however, is that the device only actuates the alarm when the pressure in the hydraulic jack rises above a certain level. Thus, this device is of little use in providing a repeated indication of reciprocating movement of a part such as a polish rod.
In view of the above, it is an object of the present invention to provide an improved device for indicating variations in load on a reciprocally moving part such as a polish rod.
A further object of the present invention is to provide an indicating device which is relatively simple and inexpensive to manufacture.
It is a further object of the present invention to provide a simple, reliable device which will provide an indication of load variation once during each cycle of the reciprocally moving part.
It is a further object of the present invention to provide an indicating device which requires relatively minimal technical sophistication to monitor.
Yet another object of the present invention is to provide an indicating device which is subjected to the full load on a reciprocating moving part to more accurately monitor the moving part.
It is a further object of the present invention to provide an indicating device which provides continuous monitoring of a reciprocally moving part.
It is a further object of the present invention to provide an indicating device which is of rugged construction and thus resistant to damage.
It is a further object of the present invention to provide an indicating device which is simple to repair when necessary.
A further object of the present invention is to provide an indicating device which is adjustable to compensate for wear on the device and for variations in a reciprocating movement of a part.
The above objects as well as other objects not specifically enumerated are accomplished by an indicating device for indicating variations in a load on a reciprocally moving part in accordance with the present invention. The indicating device of the present invention includes reciprocating moving means for reciprocatingly moving in response to the variations in the load, indicating means for providing an indication, and switch means for switching between an open state and a closed state and for causing current to flow through the indicating means when the switch means is in one of the open and closed states, wherein the reciprocating moving means causes the switch means to switch to the one of the open and closed states once during each cycle of the reciprocating movement of the reciprocating moving means.
The objects of the present invention are also accomplished by a polish rod load indicating device which includes a master piston and cylinder enclosing a fluid therebetween, wherein the master piston and cylinder are connectable to the polish rod such that one of the master piston and cylinder moves cyclically with respect to the other of the master piston and cylinder, a slave piston and cylinder enclosing a fluid therebetween which is in communication with the fluid enclosed by the master piston and cylinder, wherein the cyclical movement of the one of the master piston and cylinder produces a cyclically varying pressure in the fluids and wherein the cyclically varying pressure in the fluids causes one of the slave piston and cylinder to move cyclically relative to the other of the slave piston and cylinder, an indicator, and a switch, wherein the indicator produces a polish rod load indication signal in response to operation of the switch, and wherein the cyclically moving one of the slave piston and cylinder operates the switch to cause the indicator to produce the polish rod load indication signal once during each cycle of the cyclical movement of the cyclically moving one of the slave piston and cylinder.
The objects of the present invention are further accomplished by a polish rod load indicating device for indicating variation in a polish rod load, which includes a toroidally-shaped master piston, a toroidally-shaped master cylinder cooperating with the master piston to enclose a fluid, the master piston and cylinder being connected to a portion of the pump, a slave piston and cylinder enclosing a fluid which is in fluid communication with the fluid enclosed by the master piston and cylinder, wherein the slave piston includes a flange portion, is movable between extended and retracted positions within the slave cylinder, and is spring biased towards the retracted position, a switch, wherein the switch is movable between an open position and a closed position and is spring biased towards the open position, and an indicator, the indicator producing an indication when current flows therethrough, wherein the master piston is cyclically moveable in response to cyclical movement of the polish rod to produce a cyclically varying pressure in the fluids, and wherein the cyclically varying pressure causes the slave piston to move cyclically between the extended and retracted positions such that the flange portion of the slave piston moves the switch to the closed position when the slave piston is in the retracted position, closing of the switch causing current to flow through the indicator so that the indicator provides the indication once during each cycle of the cyclical movement of the master piston to indicate variation in the polish rod load.